The present application relates to a method of forming a Group III nitride containing semiconductor structure. More particularly, the present application relates to a method of removing, i.e., releasing, a portion of a Group III nitride material from a multilayered stack containing a Group III nitride material layer by spalling.
Group III nitride materials are a unique group of semiconductor materials which can be used in a wide variety of applications including, for example, optoelectronics, photovoltaics and lighting. Group III nitride materials are composed of nitrogen and at least one element from Group III, i.e., aluminum (Al), gallium (Ga) and indium (In), of the Periodic Table of Elements. Illustrative examples of some common gallium nitrides are GaN, GaAlN, and GaAlInN. By changing the composition of Al, Ga and/or In within a Group III nitride material, the Group III nitride material can be tuned along the electromagnetic spectrum; mainly from 210 nm to 1770 nm. This spectrum includes the visible light emitting diode (LED), which is more than a 10 billion dollar industry with a forecasted double digit yearly growth rate. This continuous growth in LED demand enables the infrastructural build-up for the growth and fabrication of Group III nitride based semiconductor devices.
One of the bottlenecks for Group III nitride based semiconductor devices is a lack of a latticed matched substrate. Some of the conventional substrates are sapphire (Al2O3), silicon carbide (SiC), silicon (Si), and zinc oxide (ZnO) that have about 13%, 3%, 17% and 2%, respectively, lattice mismatch with GaN. Currently, lattice matched freestanding GaN and AlN substrates are being developed. However, lattice matched substrates suffer from availability and cost.
Despite all the research efforts, the cost of Group III nitride containing devices is high. One way to reduce the cost is to enable reuse of the Group III nitride material.
Substrate release in Group III nitrides is currently being realized by a technique called laser-liftoff. Laser lift-off employs a high power focused laser beam to target the Group III nitride/substrate interface to melt the Group III nitride into the corresponding Group IIII element. After this laser treatment, and once heated up-to about 100° C., the Group IIII element melts releasing the substrate. This approach is slow, applies to only small areas, and requires a substrate where the laser can penetrate through without absorption so that it can be absorbed at the Group III nitride material/substrate interface. For instance, this technique cannot be employed for GaN or ZnO substrates, silicon, or silicon carbide as these materials have an optical bandgap that is close to, or smaller than, GaN material. In addition, the laser lift-off approach leads to the formation of a Group III element on the point of laser contact that degrades the substrate reusage. Further, the laser-lift approach can damage the laser exposed Group III nitride material layer.
In view of the above, a substrate release technique for a Group III nitride material system is needed to cut down costs of Group III nitride based semiconductor devices. Such a technique should (1) be applicable to large diameter wafers, (2) be industrial, convenient, and fast to execute, and (3) not damage the released epilayers or the underlying substrate.